https://en.wikipedia.org/wiki/Vacuum
https://vacaero.com/information-resources/the-heat-treat-doctor/1347-a-brief-history-of-vacuum-technology.html#:~:text=Early%20History,atomos%2C%20Greek%3A%20undividable).
Vacuum - An Introduction
Overview
In order to get introduced with Vacuum, this module has been designed for the undergraduate students studying Physics. The content has been taken form the Online resources. The purpose of this module is to learn how to prepare a module. Hence, it may not be a professional one.
Introduction to Vacuum
Vacuum
Vacuum is space (Links to an external site.) devoid of matter (Links to an external site.). The word stems from the Latin adjective vacuus for "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure (Links to an external site.) much less than atmospheric pressure (Links to an external site.). Physicists often discuss ideal test results that would occur in a perfect vacuum, which they sometimes simply call "vacuum" or free space, and use the term partial vacuum to refer to an actual imperfect vacuum as one might have in a laboratory (Links to an external site.) or in space (Links to an external site.). In engineering and applied physics on the other hand, vacuum refers to any space in which the pressure is considerably lower than atmospheric pressure. The Latin term in vacuo is used to describe an object that is surrounded by a vacuum.
Quality of Vacuum
The quality of a partial vacuum refers to how closely it approaches a perfect vacuum. Other things equal, lower gas pressure (Links to an external site.) means higher-quality vacuum. But higher-quality vacuums are possible. Ultra-high vacuum (Links to an external site.) chambers, common in chemistry, physics, and engineering, operate below one trillionth (10−12) of atmospheric pressure (100 nPa), and can reach around 100 particles/cm3. Outer space (Links to an external site.) is an even higher-quality vacuum, with the equivalent of just a few hydrogen atoms per cubic meter on average in intergalactic space. According to modern understanding, even if all matter could be removed from a volume, it would still not be "empty" due to vacuum fluctuations (Links to an external site.), dark energy (Links to an external site.), transiting gamma rays (Links to an external site.), cosmic rays (Links to an external site.), neutrinos (Links to an external site.), and other phenomena in quantum physics. (Links to an external site.) In the study of electromagnetism (Links to an external site.) in the 19th century, vacuum was thought to be filled with a medium called aether (Links to an external site.). In modern particle physics, the vacuum state (Links to an external site.) is considered the ground state (Links to an external site.) of a field (Links to an external site.). Vacuum has been a frequent topic of philosophical (Links to an external site.) debate since ancient Greek (Links to an external site.) times, but was not studied empirically until the 17th century.
Evangelista Torricelli (Links to an external site.) produced the first laboratory vacuum in 1643, and other experimental techniques were developed as a result of his theories of atmospheric pressure (Links to an external site.). A torricellian vacuum is created by filling a tall glass container closed at one end with mercury, and then inverting it in a bowl contain the mercury (see in the figure).
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Vacuum became a valuable industrial tool in the 20th century with the introduction of incandescent light bulbs (Links to an external site.) and vacuum tubes (Links to an external site.), and a wide array of vacuum technologies has since become available. The recent development of human spaceflight (Links to an external site.) has raised interest in the impact of vacuum on human health, and on life forms in general.
History of Vacuum Technology
A breif history of Vacuum Technology has been provided in the following link.
Measurement of Vacuum
The quality of a vacuum is indicated by the amount of matter remaining in the system, so that a high quality vacuum is one with very little matter left in it. Vacuum is primarily measured by its absolute pressure (Links to an external site.), but a complete characterization requires further parameters, such as temperature (Links to an external site.) and chemical composition. One of the most important parameters is the mean free path (Links to an external site.) (MFP) of residual gases, which indicates the average distance that molecules will travel between collisions with each other. As the gas density decreases, the MFP increases, and when the MFP is longer than the chamber, pump, spacecraft, or other objects present, the continuum assumptions of fluid mechanics (Links to an external site.) do not apply. This vacuum state is called high vacuum, and the study of fluid flows in this regime is called particle gas dynamics. The MFP of air at atmospheric pressure is very short, 70 nm (Links to an external site.), but at 100 mPa (Links to an external site.) (~1×10−3 Torr (Links to an external site.)) the MFP of room temperature air is roughly 100 mm, which is on the order of everyday objects such as vacuum tubes (Links to an external site.). The Crookes radiometer (Links to an external site.) turns when the MFP is larger than the size of the vanes. Vacuum quality is subdivided into ranges according to the technology required to achieve it or measure it. These ranges do not have universally agreed definitions, but a typical distribution is shown in the following table. As we travel into orbit, outer space and ultimately intergalactic space, the pressure varies by several orders of magnitude (Links to an external site.).
Atmospheric pressure is variable but standardized at 101.325 kPa (760 Torr).
Low vacuum, also called rough vacuum or coarse vacuum, is vacuum that can be achieved or measured with rudimentary equipment such as a vacuum cleaner (Links to an external site.) and a liquid column manometer (Links to an external site.).
Medium vacuum is vacuum that can be achieved with a single pump, but the pressure is too low to measure with a liquid or mechanical manometer. It can be measured with a McLeod gauge (Links to an external site.), thermal gauge or a capacitive gauge.
High vacuum is vacuum where the MFP (Links to an external site.) of residual gases is longer than the size of the chamber or of the object under test. High vacuum usually requires multi-stage pumping and ion gauge measurement. Some texts differentiate between high vacuum and very high vacuum.
Ultra high vacuum requires baking the chamber to remove trace gases, and other special procedures. British and German standards define ultra high vacuum as pressures below 10−6 Pa (10−8 Torr).
Deep space is generally much more empty than any artificial vacuum. It may or may not meet the definition of high vacuum above, depending on what region of space and astronomical bodies are being considered. For example, the MFP of interplanetary space is smaller than the size of the Solar System, but larger than small planets and moons.
As a result, solar winds exhibit continuum flow on the scale of the Solar System, but must be considered a bombardment of particles with respect to the Earth and Moon.
Perfect vacuum is an ideal state of no particles at all. It cannot be achieved in a laboratory (Links to an external site.), although there may be small volumes which, for a brief moment, happen to have no particles of matter in them.
Even if all particles of matter were removed, there would still be photons (Links to an external site.) and gravitons (Links to an external site.), as well as dark energy (Links to an external site.), virtual particles (Links to an external site.), and other aspects of the quantum vacuum (Links to an external site.).
Hard vacuum and soft vacuum are terms that are defined with a dividing line defined differently by different sources, such as 1 Torr (Links to an external site.), or 0.1 Torr, the common denominator being that a hard vacuum is a higher vacuum than a soft one.
Vacuum quality | |||
760 | 1.013×105 | 1 | |
Low vacuum | 760 to 25 | 1×105 to 3×103 | 9.87×10−1 to 3×10−2 |
Medium vacuum | 25 to 1×10−3 | 3×103 to 1×10−1 | 3×10−2 to 9.87×10−7 |
High vacuum | 1×10−3 to 1×10−9 | 1×10−1 to 1×10−7 | 9.87×10−7 to 9.87×10−13 |
1×10−9 to 1×10−12 | 1×10−7 to 1×10−10 | 9.87×10−13 to 9.87×10−16 | |
Extremely high vacuum | < 1×10−12 | < 1×10−10 | < 9.87×10−16 |
1×10−6 to < 1×10−17 | 1×10−4 to < 3×10−15 | 9.87×10−10 to < 2.96×10−20 | |
Perfect vacuum | 0 | 0 | 0 |
Rotary Pump
The function of Rotary pump has been given in the following link